I don't think a "departmental letter" is all that common in pathology. Maybe my experience isn't indicative, I dunno -- I hadn't heard of a dean's letter either until I started the application process. I think having a couple of letters from pathologists who you have rotated with/actually worked with is what you need most, as it shows you have an idea of what you're getting into and aren't so terrible that no-one will give you a rec. A recognized name, professor, or department head helps, but I don't know that a so-called department letter would -- I suppose if it's good, and not one of those boringly honest ones like what I've seen of dean's letters. Otherwise LOR's just need to not be terrible. Everyone knows that almost no-one writes a completely honest or critical LOR, and the few who do tend to be blown off a bit as those classic hard-a55es who refuse to be completely pleased by any student. That's why it's called a letter of *recommendation*.
Having said all of that, I think it's a good idea to get any letter of recommendation you can, if you can choose -later- which ones to send to who. Some will let you read their letters, and that will help you make the decision of which ones to use. Some will never get around to writing the letter you were counting on. Most will give you a reasonable idea what kind of letter they write, even if they don't exactly spell it out for you, just by what they ask you about, etc. But heck, some will end up letting you write the letter before they review it and sign it.
